Date Available

4-3-2012

Year of Publication

2011

Degree Name

Master of Science (MS)

Document Type

Master's Thesis

College

Arts and Sciences

Department/School/Program

Earth and Environmental Sciences (Geology)

First Advisor

Dr. Alan E Fryar

Abstract

Multiple studies in the Bengal basin have shown that elevated As in groundwater coincides with reduced, relatively dark sediments of Himalayan provenance. In West Bengal state (India), As concentrations > 10 μg/L tend to occur east of the River Bhagirathi-Hoogly, the main distributary of the Ganges. Associations among sediment chemistry and mineralogy for four cores from either side of the Bhagirathi-Hoogly (cores 1 and 2 to the east, 3 and 4 to the west) in Murshidabad district were investigated. Ten sediment samples were collected from each boring at various depths to a maximum of 38 to 43 m. Sediment chemistry was investigated using sequential extraction, digestion and analysis of As, Al, Ca, Fe, and Mn on an ICP-OES and GFAAS, and by total carbon analysis on a CNS analyzer. Organic carbon content was measured gravimetrically by HCl digestion. Sediment mineralogy was investigated using thin-section petrography and a microprobe EDS. Pyroxenes and phyllosilicates appear to be the primary sources of arsenic in the study area. Additionally, core 4 sediments are mineralogically similar to cores 1 and 2 despite differences in arsenic concentrations in the groundwater. We conclude that a 65-ft (20-m) silt layer overlying the aquifer sands in core 4 acts as a local aquitard and restricts arsenic mobilization locally.

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